POWDERY PRODUCT COMPRISING FINELY DIVIDED ALKALI SILICATE AND PROCESS FOR PRODUCING THE SAME

Abstract: The present invention relates to a finely-powdered, storage-stable powder-like product containing alkali silicate and a production method thereof. Said alkali silicate is used, inter alia, as an ingredient reinforcing cement, mortar or paint and to provide waterproofing. According to the present invention, for a solid, glassy alkali silicate mass a mechanical grinding is performed for changing the mass into rapidly water-soluble powder with particle size below 100 mu m, whereafter a finely-powder, non-hygroscopic stabilizer is mixed in the powder to prevent the product from caking. For the stabilizer, inter alia, light aluminium silicate pearls nonsoluble in water and extremely finely-powdered quartz powder can be conceivable. A product containing alkali silicate and stabilizer can according to the invention be included as an ingredient in dry, finely-powdered mortar, cement or paint, whereby they can be brought into useful, hardening state merely by adding water on the site.

Description: POWDERY PRODUCT COMPRISING FINELY DIVIDED ALKALI SILICATE AND PROCESS FOR PRODUCING THE SAME. The present invention relates to a storage-stable finely- powdered product comprising finely powdered alkali silicate, and a process for producing said product. Alkali silicates, such as water-glass Na 2 0-nSi0 2 and potassic water-glass K 2 0*nSi0 2 in which n = 3-4, are used e.g. in mortars, cements and paints as a reinforcing ingredient and for providing waterproofing. According to the technology known in the art, the alkali silicates have been brought into finely powdered form by through-drying of the silicate sol¬ ution. Such through-drying is described, inter alia, in GB application publication No. 2 086 402 and in publication FI- 426 578. A problem of through-dried alkali silicate has been the re¬ latively slow dissolution in water. It may even take about twenty-four hours for silicate particles before being com¬ pletely dissolved, which in practice means that said par¬ ticles cannot be included as ingredients in dry powderized mortar, cement or paint. For that reason, silicates have been used in prefabricated solutions to be mixed on the site with other, solid ingredients of a hardening mixture. The slowness of the dissolution of the through-dry silicate becomes ob¬ vious in the table on page 3 in GB patent application No. 2 086 402, according to which the increase of viscosity brought about by gel-formation following the dissolution was very in- significant in the five first minutes, more visible in half an hour, but the final stage was not reached until about twenty-four hours later. According to the publication, a gel- forming agent was used as an aid, such as sodium silicone fluoride. According to examples 5 and 6 of the Finnish pub- lication No. 426 578, in a produce containing through-dried sodium silicate powder the gel-formation took place within about quarter of an hour or 1 hour. The objective of the present invention is to provide a sol¬ ution for introducing alkali silicate into powderized form in which it is dissolved in water substantially more rapidly than the current through-dry silicates, whereby it can be in- eluded as an ingredient in a powder-like product to be hard¬ ened, such as mortar or paint, without having to take resort to an additive to accelerate solubility or gelformation. The production method of a powderized product containing alkali silicate is according to the invention characterized in that mechanical grinding is performed for solid, glassy alkali silicate mass for transforming the mass into a powder dis¬ solving rapidly in water, the particle size of said powder being below 100 μm, and that finely-powdered, non-hygroscopic stabilizer is mixed in the powder for preventing the product from caking. Different from blow-dry silicate powder, the silicate powder produced by mechanical grinding as taught by the present in¬ vention is rapidly water-soluble. According to the experi- ments, the powder is completely solved in cold water in about 2 or 3 minutes without any need for an additive to advance the dissolution. The silicate content of the solution thus obtained can be about 40 per cent by weight, although a con¬ centration of about 1 to 5 per cent by weight is in general adequate in practical applications. The alkali slicate powder produced by mechanical grinding, externally resembling, when finest, wheat or potato flour (average particle size below 1 μm) , is characterized by hygroscopy, because of which it owing to the moisture in the air starts to cake and finally becomes similar to the glassy mass as the one wherefrom the powder was made of. In order to prevent said procedure to happen, according to the present invention in the alkali silicate powder a finely-powdered stabilizer is added to keep the powder running and thus ap¬ propriate for storing. A mixture of silicate powder and stabilizer according to the present invention can be mixed into an ingredient of a dry, finely ground mortar, cement or paint, whereby only water needs be added on the site to pro¬ vide a mass ready for use. The dissolution of the silicate powder and gel formation is shown in instantly started pre- cipitation of the mass. The mortar, cement or paint produced according to the present invention is characterized by relatively rapid solidification after addition of water. Particularly in paints said property inhibits harmful running on vertical surfaces. A solid, glassy silicate mass, ground according to the in¬ vention, can be prepared e.g. by drying from silicate in sol¬ ution form, said silicates being commercially available. The grinding can be carried out e.g. between grinding stones or by any other grinding method of mineral matter known in the art. The quality of finely-powdered stabilizer added according to the present invention in alkali silicate powder may vary, as based on the initial tests. The essential feature is that the stabilizer in itself is not hygroscopic and that it keeps the ground silicate particles sufficiently apart from one another to prevent them from adhering to each other. Hollow glass pearls not soluble in water and made from aluminium silicates have proved to be highly useful for said purpose, their par¬ ticle size being about 50 to 300 micrometer. One such product is e.g. Enlett 300 marketed by Nordiska Mineralprodukter Ab, the maximum particle size whereof being 300 μm, average par- tide size 75 μm, density 0.20 g/cm 3 , and being capable of absorbing moisture of 0.4 per cent by weight. Such stabilizer can be mixed in alkali silicate as an amount of about 40 to 55 per cent by weight. An appropriate mixing ratio has been found to be 50 per cent by weight of the stabilizer and 50 per cent by weight of the alkali silicate. The aluminium silicate stabilizer is nonsoluble in water, but it keeps the alkali silicate particles dry and running, and after adding water, rapidly water-soluble. Another stabilizer found to be efficient is a highly finely powdered quartz powder with less than 0.1 μm particle size, most preferably about 2 to 40 nm particular size. The effect of said stabilizer particles is assumed to be based on the fact that they form a protective skin around alkali silicate particles of substantially greater size, so preventing them from absorbing moisture and adhering to each other. Less of a stabilizer acting in said manner is needed, about 3 to 10 per cent by weight, preferably about 5 per cent by weight of the quantity of the alkali silicate. As an example of approriate finely-powdered quartz powders can be mentioned Aerosil pro¬ ducts marketed by Degussa AG, a variety of which being co - mercially available, both hydrophobic and hydrophilic, but all whereof being mainly silica dioxide, with an average particle size in the range 7 to 40 nm. As regards the pre¬ sent invention, particularly the hydrophilic types, such as Aerosil 200, are preferred. In a product according to the present invention, stabilizers of several different types may also be included simultaneous¬ ly. It is possible, for instance, to prepare waterglass par¬ ticles by grinding mechanically, in which aluminium silicate pearls (Enlett) and highly finely powdered quartz powder (Aerosil) are added, their particle size being of the same order of magnitude. The composition of the mixture may in such case be as follows: 45% alkali silicate, 50% Enlett 300, and 5% Aerosil 200. As described above, a product according to the present in¬ vention, containing alkali silicate, is characterized in that it contains solid, mechanically ground water-soluble alkali silicate with particle size of below 100 μm, preferredly 0.1 to 10 μm, and in which finely powdered, non-hygroscopic stab¬ ilizer is mixed for preventing it from caking. As regards various embodiments of the product, reference is made to what is described above and to the accompanying claims. Example 1 An aqueous solution of sodium silicate was dried into solid, glassy waterglass, which was subjected to mechanical grinding into below 100 μm particle size. The waterglass powder thus obtained was mixed into 5 per cent by weight of commercially available, powder-like Portland dry cement. 40% water of the amount of the cement was added in the mixture so that it be¬ came loose, running gruel. After one minute of water addition thickening seen with a naked eye could be observed in the mixture, in two minutes it had become porridge-like, and in 5 minutes, thick putty. The test proved the rapid dissolution of the mechanically ground waterglass, and the gel-formation thereafter. Example 2 The procedure as in Example 1, but instead of waterglass potassic waterglass, which was potassic silicate, was used. The result of the test was the same as in Example 1, i.e. in about 5 minutes the mixture of mechanically ground potassic waterglass and water had become thick and putty. Example 3 (reference example) In dry cement, being the same as in Example 1, 5 per cent by weight of through-dried silicate powder Portil N produced by Ahlsell Mineral AB, which is chemically waterglass Na 2 0 . 3.3 Si0 2 . Water was added in the mixture in the way of Example 1, that is, so that loose, running gruel was obtained. No visible change could be discerned in the viscosity of the gruel in a half an hour. The test was repeated using through-dried silicate powder Portil A of Ahlsell Mineral AB which contained more sodium compared with silica. The result of the test was precisely the same, no change in viscosity could be observed in half an hour. Example 4 50 per cent by weight of waterglass powder ground as in Example 1 and 50 per cent by weight of produce Enlett 300, hollow aluminium silicate pearls with 75 μm average particle size, were mixed. It resulted in a running, powder-like pro¬ duct. The product was stored in ordinary room air for 6 months. After the storage, 5 per cent by weight of the pro¬ duce, which had remained as a running powder, was mixed in cold water. In less than 2 minutes the waterglass had dis- solved completely and the aluminium silicate had been sep¬ arated as a nonsoluble ingredient on the water surface. It is obvious to a person skilled in the art that various embodiments of the invention are not limited to the examples presented above, and they may be varied within the scope of the accompanying claims.

Claims: Claims 1. A process for producing storage-stable product comprising finely-powdered alkali silicate, characterized in that mechanical grinding is performed for solid, glassy alkali silicate for turning the mass into a rapidly water-soluble powder, with less than 100 μm particle size, and that finely- powdered, non-hygroscopic stabilizer was mixed in the powder for preventing caking of the product. 2. Process according to claim 1, characterized in that the alkali silicate is waterglass or potassic waterglass, or a mixture thereof. 3. Process according to claim 1 or 2, characterized in that the stabilizer consists of hollow glass pearls nonsoluble in water, their particle size being about 50 to 300 μm. 4. Process according to claim 3, characterized in that the mixing ratio of alkali silicate and aluminium silicate is 45 to 60 per cent by weight, preferably about 50 per cent by weight, of alkali silicate, and 40 to 55 per cent by weight, preferably about 50 per cent by weight, of aluminium sili¬ cate. 5. Process according to claim 1 or 2, characterized in that the stabilizer is quartz powder with particle size below 0.1 μm, preferably about 2 to 40 nm. 6. Process according to claim 5, characterized in that the amount of quartz is 3 to 10 per cent by weight, preferably about 5 per cent by weight, of the alkali silicate amount. 7. Process according to any one of the preceding claims, characterized in that a mixture of alkali silicate and stabilizer is included in mortar, cement or paint as an ingredient thereof. 8. Storage-stable, powder-like product containing finely powdered alkali silicate, characterized in that it contains solid, mechanically ground, water-soluble alkali silicate, the particle size thereof being below 100 μm, advantageously 0.1 to 10 μm, and in which a finely-powdered, non-hygroscopic stabilizer has been mixed for preventing it from caking. 9. Product according claim 8, characterized in that the al¬ kali silicate is waterglass or potassic water glass, or a mixture thereof, that the stabilizer consists of hollow, in¬ soluble glass pearls made from aluminium silicate, their par¬ ticle size being 50 to 300 μm, and that the mixing ratio of alkali silicate and aluminium silicate is 45 to 60 per cent by weight, preferably about 50 per cent by weight, of alkali silicate, and 40 to 55 per cent by weight, preferably about 50 per cent by weight, of aluminium silicate. 10. Product according to claim 8, characterized in that the alkali silicate is water glass or potassic water glass, or a mixture thereof, that the stabilizer is quartz powder, the particle size thereof being at most 0.1 μm, preferably about 2 to 40 nm, and that the amount of quartz is 3 to 10 per cent by weight, preferably about 5 per cent by weight, of the amount of alkali silicate.

Inventors: VALORANTA PENTTI, VALORANTA, PENTTI
Applicants: FROM KENNETH, VALORANTA PENTTI, FROM, KENNETH, VALORANTA, PENTTI
Application year: 1994
Main classification: C01B33
IPC codes: C01B33, C04B12, C04B28, C09D1